Various types of domestic drinking water purification systems, which claim to provide microorganism-free filtered water, are known in the art. The most commonly used systems remove protozoan cysts, such as cryptorsproridium Parvum and giardia Lablia, which may be found in insufficiently chlorinated water supplies. As the cysts are from 5–10 microns in size, they are typically removed by a one micron rated microporous filter element, usually fabricated from carbon block, so that it simultaneously removes chlorine and other impurities to improve taste. Submicron microporous filters fabricated from ceramic or synthetic polymeric materials, with a maximum pore size of 0.2 micron, are also known. Such filters are capable of removing pathogenic bacteria such as pseudomonas Aurigena, which may also be found in domestic, treated water supplies. The danger is that the users of such filters may be given a false sense of security at times when such organisms are discovered in the local water supply and a “boil water” alert is issued by the authorities. Although several such filters may be performance-tested when certified for the validity of their claims, few, if any, claim to 100% quality assure every filter unit sold. Thus, some finite fraction of units sold do not in fact meet the claimed retention. In addition, the filter element might either have been damaged prior to being installed, or might be improperly installed by the user in the housing, such that leakage of unfiltered water into the final product is possible. Finally, glue seals to the filter in the fabricated filter element can sometimes fail over time in an aqueous environment, depending on factors such as pH and temperature and the number of mechanical shocks given to the system during opening and closing the water supply to the system. In all of the above instances, since such purification systems do not comprise means for testing the integrity of the filter, the user has no way to verify if the system will in fact perform according to claimed performance specifications.
Means for testing filter integrity are also known in the art. Thus, U.S. Pat. No. 4,872,974 discloses a membrane filter testing method, which comprises increasing the pressure at the primary side of a membrane filter fixedly accommodating the housing and wetted with a liquid, by a gas at a predetermined rate, and checking whether the pressure at the primary side of the membrane filter is within a specified judging range after the lapse of a predetermined period of time.
U.S. Pat. No. 5,417,101 discloses a method and apparatus for isolating defective filter elements by measuring a gas flow rate under known pressure conditions through said elements.
U.S. Pat. No. 5,594,161 discloses a method of testing the integrity of a filter element in a filter assembly which includes wetting the filter, subjecting the inlet side of the filter to a gas pressure, measuring the pressure in the outlet conduit as a function of time, and determining whether a pressure measurement at a preselected time exceeds a reference pressure by a predetermined amount.
An article entitled “Predicting . . . Removal Performance of membrane Systems using In Situ Integrity Testing”, published in Filtration and Separation, January/February 1998, pp. 26–29, describes two main methods for testing membrane systems integrity, the first of which consists in applying air at a pressure bubble point to one side of the membrane, isolating and then measuring the declining pressure over time. The bubble point hereinbefore referred to, or more exactly, the bubble point pressure, is defined as the pressure required for forcing the air to flow through the pores of a membrane whose pores have been initially completely filled by a liquid. The other method consists in filling the shell of the module with a liquid and allowing the air leakage to displace liquid from the shell. The flow rate of displaced liquid is then a direct measure of the membrane integrity.
The testing methods of the prior art, as summarized hereinbefore, and in general, all the methods of the art, require the measurement of a physical quantity, be it a volume or a pressure, and therefore, a certain degree of expertise on the operator's part and the presence of the required measurement components. They are, therefore, unsuited to a domestic drinking water apparatus. On the other hand, domestic apparatus should be provided with methods for testing the integrity of filter, to avoid the danger of a supply of unsafe water.
It is therefore a purpose of this invention to provide a domestic water-dispensing apparatus that is provided with the means for testing the integrity of the filter.
It is another purpose of the invention to provide a domestic water-dispensing method and apparatus that do not require the measurement of physical quantities, and judge the integrity of the filter by visual inspection or by sensing of a physical property for the presence of air bubbles.
It is a further purpose of this invention to provide such a method, system and apparatus that are simple and of simple and secure operation and require no expertise on the user's part.
It is a still further purpose of this invention to provide a domestic water-dispensing apparatus, comprising means for determining the filter integrity, which are simple in structure and operation and economical.
It is a still further purpose of this invention to provide a domestic water-dispensing apparatus, comprising automatically controlled means for determining the filter integrity.
Other purposes and advantages of the invention will appear as the description proceeds.